Device for monitoring the unbalance of the electric power demanded

Abstract

A device for monitoring the unbalance of the electric power demanded on the conductive lines of an alternating current network of a three-phase internal installation. The device applies to all networks or three-phase installations which serve single-phase type devices in terms of variable number and power.

What is claimed is: 
     
       1. A device to monitor the unbalance of the electric power demanded on the conductive lines of a network or three-phase alternating electrical installation, said network including one line for each phase and a return current neutral line, wherein said device comprises a means to measure the currents connected to the lines of the network so as to supply on respective outputs the numerical values of the currents circulating in these lines, a means to calculate the value of the ratio, at a given instant of the value of the current circulating in the neutral line, to the sum of the values of the currents circulating in the phase lines, a numerical signal representative of the value of the ratio being supplied on one output of the calculation means, a first indication means connected to the output of the calculation means so as to indicate when the value of said ratio exceeds a predetermined unbalance threshold, while the power demanded at the same moment itself is greater than a certain proportion of the power assigned, and a second indication means connected to the outputs of the means for measuring the currents in the phase lines and to one output of the first indication means so as to localize the phase line in which a current is circulating whose value is greater than each of the values of the currents circulating in the other phase lines, the localized line being the one which has caused the unbalance. 
     
     
       2. The device according to claim 1, wherein the first indication means comprises a threshold detector connected to the output of the calculation means, one output of the detector being connected to a first indicator which changes state as soon as said predetermined threshold is exceeded. 
     
     
       3. The device according to claim 2, wherein the second indication means comprises a comparator having inputs connected to the outputs of the means for measuring the values of the currents in the phase lines, so as to determine at each instant the phase line in which a current is circulating whose value is greater than the values of the currents circulating in the other phase lines, the comparator having outputs respectively corresponding to the phase lines, a coded signal, corresponding to the line in which a current of greater value is circulating, being supplied on the corresponding output of the comparator, a selective logic circuit having inputs connected to the outputs of the comparator and to the output of the threshold detector, the selective logic circuit having outputs corresponding to the phase lines, said outputs respectively being connected to a plurality of second indicators, the logic circuit, as soon as said predetermined threshold is exceeded, selecting the indicator corresponding to the line in which the higher value is circulating. 
     
     
       4. The device according to claim 3, and further comprising a recording means connected to the output of the calculation means and to the output of the threshold detector so as to record the values of said ratios each time the predetermined threshold is exceeded. 
     
     
       5. The device according to claim 4, wherein the recording means are connected to the outputs of the means for measuring the values of the currents in the phase lines, and to the outputs of the selective logic circuit so as to record, on each occasion the predetermined threshold is exceeded, the upper value of the current in the phase line having caused this unbalance.